This invention relates to multiple turbine-generator control systems for hydroelectric power installations.
Power control systems for hydroelectric turbine driven generators generally involve the internal regulation of turbine operation. Operation of two or more hydraulic turbines are, for example, regulated through inflow valves or gates for speed and power control purposes to match load demand according to U.S. Pat. No. 4,245,163 to Philippe. According to U.S. Pat. No. 3,848,171 to Speth, turbine blades are adjusted automatically under variable flow conditions to obtain maximum efficiency. A speed controlling valve of gate is utilized for turbine control in a feedback mode of operation in a hydroelectric power environment according to U.S. Pat. No. 3,556,668 to Murbukh.
Load sharing, multiple turbine driven generators are disclosed in U.S. Pat. Nos. 4,164,661, 4,195,231, 3,651,331 and 3,703,663. None of the turbines disclosed in the foregoing patents are associated with the variable flow, hydropower sources since the control systems are usually designed to meet load demand. The use of a control system to match turbine performance with load for maximum efficiency is taught in U.S. Pat. No. 3,300,647 to Gogia.
Despite the availability of various prior art multiple turbine-generator power generating systems as referred to herein, there are certain drawbacks in such systems for which there is a renewed interest for small scale hydroelectric power generating plants, below 5 megawatts, for example. The turbine-generator adjustments necessary to meet varying water flow rates are costly and less than satisfactory for such small scale hydropower plants because of reduced turbine efficiency. The usual hydraulic turbine, for example, having provisions for adjusting flow to handle flow decreased to a lower limit of 30% of rated flow, will have a reduced efficiency of 80% to 85% of its design efficiency. The ability to handle varying flow is necessary because a 100% continuous flow condition is rarely found in hydropower sites. As to fixed hydraulic geometry turbines that are less costly and capable of being mass produced, use thereof is not now deemed to be a viable alternative because of a drop in rated efficiency to 80% of rated value at 80% of rated flow and toward zero efficiency at 40% of rated flow.
It is therefore an important object of the present invention to provide a more cost effective and efficient hydroelectric power plant, especially useful for small hydropower sites, utilizing a plurality of less costly fixed geometry hydraulic turbines operating with maximum efficiency despite varying flow conditions.